We propose to add a three laser, high-speed cell sorter (Cytomation MoFlo) that is capable of using any combination of visible-excited fluorescent reagents up to a total of eleven different dyes. Recent developments in new dyes, instrumentation and software, largely carried out by researchers in the Stanford Shared FACS Facility (SSFF), have made it feasible to evaluate up to 11 fluorescent markers on each cell in flow cytometric measurements. Paradoxically, the use of more fluorescence colors often simplifies the data by resolving previously unrecognized heterogeneities. The SSFF is a center for development of new cytometry applications, particularly in the areas of multicolor analysis and sorting. Many of the current users of the Facility are already doing work that would benefit from the capabilities of the new instrument, and others are poised to take advantage of extended multi-color fluorescence analysis and high speed cell sorting. At present, the SSFF is approaching saturation in use of its three cell sorters, and it makes sense to add an instrument that provides the most additional capacity to the Facility. The specific contribution of the new instrument will be to (1) support new research applications with extended instrumentation capabilities that are not available with the existing Facility cell sorters, particularly high-speed sorting in combination with up to 11-color fluorescence analysis, and (2) expand the availability of state-of-the-art flow cytometry and cell sorting to the research community at Stanford. The new sorter will not only improve the quality and availability of experimental work that is already possible in the Facility, it will extend capabilities in ways that can be immediately utilized by a number of the ongoing research programs served by the Facility. The new instrument will be integrated into an existing research core facility, which will operate, maintain and administer it within Stanford University cost center guidelines. Since its establishment in 1985 as a Stanford University "cost center" the Shared FACS Facility has met its full operating budget out of user fees. Almost all the work done in the Stanford Shared FACS Facility is health related research ranging from basic studies in molecular biology, genetics and development to AIDS-related clinical research. The large majority of the work in the Facility is NIH supported.